Electromagnetic distance relay with an offset mho operating characteristic



Aug. 5, 1958 Filed Aug. 5, 1956 C G. DEWEY ELECTROMAGNETIC DISTANCE RELAY WITH AN OFFSET MHO OPERATING CHARACTERISTIC 3 Sheets-Sheet 1 UV 1 u l 3/ z: 3 524 Inventor: Clyde 6. Dewey.

Aug. 5, 1958 c. G. DEWEY ELECTROMAGNETIC DISTANCE RELAY WITH AN OFFSET MHO OPERATING CHARACTERISTIC 3 Sheets-Sheet 2 Filed. Aug. 3, 1956 Inventor:

Glide G. Dezeg,

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Aug. 5, 1958 c. G. DEWEY 2,846,620

ELECTROMAGNETIC DISTANCE RELAY WITH AN OFFSET MHO OPERATING CHARACTERISTIC Filed Aug. 5. 1956 3 SheetsSheet 3 Inventor: Clgde G. Dewey,

United States Patent ELECTROMAGNETIC DISTANCE RELAY WITH AN OFFSET MHO OPERATING CHARACTERISTIC Clyde G. Dewey, Philadelphia, Pa., assignor to General Electric Company, a corporation of New York Application August 3, 1956, Serial No. 601,883

' 17 Claims. Cl. 317-36) This invention relates to electromagnetic relays and more particularly to an electromagnetic induction relay of the distance type having an offset mho operating characteristic.

Distance relays are used in the art of protective relaying to perform rapid and accurate circuit controlling operations in response to predetermined relationships between alternating currents and voltages derived from a protected electric power transmission system. Such a relay is said to have an offset mho operating characteristic when its operation is controlled by the resultant of three quantities dependent, respectively, upon the transmission line voltage squared, the transmission line current squared, and the product of the voltage and current magnitudes and a function of the phase displacement therebetween. It has been the practice in this art to obtain an ofiset mho operating characteristic by supplying the windings of an electromagnetic induction relay with two electrical input quantities, one being proportional to the transmission line current and the other comprising the combination of a voltage proportional to the transmission line voltage and a biasing potential proportional to the transmission line current. The windings of the conventional relay are arranged and connected whereby opposing torques are produced in the movable induction element of the relay: an operating torque dependent upon the product of the magnitudes of and a 378 (1946). However, until now, I am unaware of any convenient and economic arrangement of windings on an electromagnetic relay of relatively simple construction whereby an offset mho operating characteristic is inherently obtainable without resort to external combination or modification of the transmission line current and voltage quantities supplied to the relay.

Accordingly, it is an object of this invention to provide an electromagnetic distance relay having an offset mho operating characteristic when supplied by two independent electric quantities representing pure transmission line current and voltage respectively.

Another object of the invention is the provision of an electromagnetic relay, supplied by only two electric quantities, having an operating characteristic which is dependent upon the square of the magnitude of one quantity, the square of the magnitude of the other quantity, and the product of both magnitudes and a function of the phase displacement therebetween.

A further object is to provide a relatively low cost 2,846,620 Patented Aug. 5, 1958 ice and small-size relay comprising an arrangement of windings on a standard four-pole electromagnetic structure supplied with alternating current and voltage, said windings being connected in a manner whereby an otfset mho operating characteristic is obtained.

In carrying out my invention in one form, I provide an electromagnetic relay comprising a frame or stator which includes a closed magnetic circuit and a plurality of salient poles projecting therefrom. A magnetizable core is spaced apart from the extremities of the salient poles to define a plurality of gaps, and a circuit controlling current conducting rotor is disposed for rotation through all of the gaps in a direction generally transverse to the magnetic fields between the poles and the core. A plurality of primary windings is provided on the stator, and these windings are connected for energization to alternating current and voltage input terminals, thereby to produce magnetic fluxes in the stator and to establish magnetic fields in the gaps. At least two shading windings are also disposed on the stator for retarding a portion of the total magnetic flux produced by each of the primary windings. I arrange the primary and shading windings on the stator whereby driving torque, which is produced by the interaction of the magnetic fields in the rotor, comprises a component proportional to the square of the magnitude of the alternating current, a component proportional to the square of the magnitude of the alternating voltage, and a component proportional to the product of the respective magnitudes of the two alternating quantities and a function of the phase displacement therebetween. In accordance with one aspect of my invention, the windings are arranged whereby the current-squared component of torque opposes the voltage-squared component, while in another aspect of my invention these two torque components are in aiding relation.

My invention will be better understood and further objects and advantages will be apparent from the following description taken inconjunction with the accompanying drawings in which:

Fig. 1 is a schematic diagram of one embodiment of my invention;

Fig. 2 is a schematic diagram of another embodiment of my invention;

Fig. 3 is a perspective diagram illustrating the production of driving torque in a relay rotor;

Fig. 4a is a schematic representation of a simple electromagnetic circuit;

Fig. 4b is a vector diagram of mmfs in a circuit of Fig. 4a;

Fig. 4c is a schematic representation of an electric circuit equivalent to the magnetic circuit of Fig. 4a;

Figs. 5a and 6a are schematic representations of the Fig. 1 embodiment of my invention showing the magnetic t fields produced by the voltage and current energized windings respectively;

Figs. 5b and 6b are equivalent electric circuit diagrams of Figs. 5a and 6a respectively;

Figs. 7a and 8a are schematic representations of the Fig. 2 embodiment of my invention showing the magnetic fields produced by the voltage and current energized windings respectively;

Figs. 7b and 7c are equivalent electric circuit diagrams of Fig. 7a;

Figs. 8b and 8c are equivalent electric circuit diagrams of Fig. 8a;

Fig. 9 is a vector diagram illustrating typical phase rela tionship between the significant voltage, current and magnetic flux quantities of my invention; and

Figs. 10 and 11 are explanatory diagrams showing the operating characteristics, in terms of impedance, of the Fig. 1 and Fig. 2 embodiments, respectively, of my invention.

Referring now to Figs. 1 and 2 of the drawings, the two schematically illustrated embodiments of my invention each comprise a frame structure or stator 12 constructed of laminated magnetizable material and having four successively adjacent spaced apart salient poles 13, 14, 15, and 16. The body of stator 12 forms a closed magnetic path or loop which is effectively divided into four consecutive sections or quarters 17, 18, 19, and by the four salient poles. Preferably the poles project from the stator body toward a centrally located axis 21 and terminate in inwardly disposed concave pole faces.

A magnetizable member or core 22 is located intermediate the salient poles 13-16 and is spaced apart from their extremities to define therewith four gaps A, B, C, and D, respectively, disposed at radial intervals with respect to axis 21. The core, which preferably is a cylindrically-shaped member physically annexed to the stator although magnetically isolated therefrom, provides a common link in the complete magnetic circuit for magnetic flux issuing from the extremities of the poles.

An electroconductive' armature or rotor 23 is mounted pivotally about axis 21 for 360 degrees rotation in the gaps A-D formed by core 22 and the faces of the four stator poles 1316. A portion of the surface of this current conducting induction element 23 is movable in overlapping relation with and generally parallel to the pole faces, and thus the current conducting path lies substantially transverse to the magnetic fields between the pole faces and the core. As will be explained in detail hereinafter, rotor 23 is actuatable in either direction by driving torque created by the interaction of the magnetic fields in the rotor. Rotation of the rotor in a given direction can be made to open or close a suitable switch contact, not shown, for the performance of a circuit controlling operation. Although as shown, rotor 23 perferably is a light-weight independent cup-shaped member which fits loosely on the cylindrical core 22, these two elements could be combined in a single, integral rotating member.

The mechanical structure of the relatively compact stator and rotor described thus far is well known in the art, as is exemplified by the structure described and claimed in United States Patent Re. 21,813 reissued on May 27, 1941, to Victor E. Verrall. It should be clearly understood, however, that my invention is not limited by the use of such specific relay construction. For example, the well known induction-disk type of electromagnetic relay structure could be utilized in connection with my invention.

As can be seen in Figs. 1 and 2, various electrical windings are disposed on stator 12. These windings include a pair of interconnected primary windings I and I which are connected in series circuit relation directly to a pair of input terminals 24 and 25, and a pair of interconnected primary windings E and E which are connected in series circuit relation directly to another pair of input terminals 26 and 27. A pair of shading windings S and S each comprising either a single ring or a plurality of endless turns of current conducting material are also located on the stator. The primary windings when energized by electric quantities supplied to the input terminals produce in stator 12 magnetic fluxes proportional to the quantities supplied. The function of the shading windings, as will be explained in detail hereinafter, is to shade or retard the magnetic fluxes traversing the parts of the stator upon which these shading windings are mounted.

The input terminals 24 and are connected to a pair of interconnected current transformers 28 and 29 associated respectively with a pair of conductors 30 and 31 which represent two lines of a 3-phase, 3-wire alternating electric power transmission system. Thus, current transformers 28 and 29 derive alternating current proportional to the transmission line current and supply this quantity to terminals 24 and 25 for energizing primary windings I and 1:. On the other hand, the input terminals 26 and 27 are connected by means of a phase shifting network 32 to a potential transformer 33. The potential transformer 33 is coupled to transmission line conductors 30 and 31. The alternating voltage derived from the transmission line voltage by potential transformer 33 is operated upon by the phase shifting network 32 and supplied to terminals 26 and 27 for energizing primary windings E and E;.

In each of the illustrated embodiments of my invention I have shown only a single relay electrically coupled to a single phase of an alternating current transmission system. This relay will respond only to transmission line faults or short circuits involving the illustrated pair of conductors 30 and 31. To obtain a complete 3-phase protective relaying arrangement, it would be necessary similarly to couple two additional identical relays to the other two phases of the 3-phase system.

The phase shifting network 32 is used to control the phase relationship between the current which flows in the primary windings E and E and the transmission line voltage. Any suitable means could be used to perform this desired controlled phase shifting function. As shown in Fig. 1 and 2 for the sake of illustration, network 32 preferably comprises a capacitor 34 connected in parallel circuit relationship with the series connected windings E and E and a resistor 35 connected in parallel circuit relationship with a capacitor 36, the two parallel circuit combinations being connected in series circuit relationship with each other across the secondary winding of the potential transformer 33. The values of resistance and capacitive reactance in this circuit can be suitably selected whereby current flowing in the inductive reactance path of the windings E and E, connected between terminals 26 and 27 is displaced from the transmission line voltage by a predetermined phase angle 0. The advantage of the particular phase shifting circuit illustrated is that it can be tuned to resonate at power system frequency whereby current will continue to flow in primary windings E and E, for two or there electrical cycles after the transmission line voltage suddenly is reduced to zero. This provides the so-called memory action. The phase shifting circuit 32 which has been illustrated is fully described and claimed in United States Patent No. 2,287,504 issued to A. R. van C. Warrington on June 23, 1942.

The specific arrangements and connections, in accordance with my invention, of the windings on stator 12 will now be considered. In the Fig. 1 embodiment of the invention, the two shading windings S and S, are located on alternative or non-adjacent poles 14 and 16 respectively, thereby to retard the magnetic fluxes in these diametrically opposed poles. Primary windings I, and I, are mounted on alternative stator sections or quarters 20 and 18 respectively, while the primary windings E and E, are located on the intermediate sections 17 and 19, respectively.

As shown in Fig. 1, the two primary windings I and I,

establish magnetic fluxes in the closed magnetic circuit of stator 12 when energized by current derived from the transmission line by current transformers 28 and 29. These windings are wound in a manner to produce opposing magnetic fluxes in the closed magnetic circuit. That is, when energizing current is flowing in the circuit of these interconnected windings in a given instantaneous direction, such as from input terminal 24 to input terminal 25, the magnetic flux produced by winding I, will be in a direction (clockwise as viewed in Fig. 1 for the specified current direction) opposite to the direction of flux produced by winding 1, (counterclockwise). Similarly, the two primary windings E and E, are wound in a manner to establish opposing magnetic fluxes in the closed magnetic circuit when energized by current from potential transformer 33. When the voltage applied across these interconnecting windings has a given instantaneous polarity, such as input terminal 26 positive with respect to input terminal 27, the flux produced by winding B; will be in a direction (counterclockwise as viewed in Fig. l for the specified voltage polarity) opposite to the direction of flux produced by winding E, (clockwise).

In the Fig. 2 embodiment of my invention, the shading windings S and S: are arranged on alternative or nonadjacent sections or quarters 18 and 20 respectively to shade the magnetic fluxes in these portions of the magnetic loop provided by stator 12. Primary windings I and I, are disposed respectively on the intermediate section 19 and on pole 14 which provides one defining boundary for the other intermediate section 17. The primary windings E and E: are mounted respectively on the intermediate section 17 and on pole 16 which comprises one of the defining poles of intermediate section 19, pole 16 being diametrically disposed with respect to pole 14.

As can be seen in Fig. 2, the two primary windings I, and I, are wound whereby with energizing current flowing from terminal 24 to terminal 25, winding 1; produces magnetic fiux in the closed magnetic circuit of stator by pole 39, the-flux density fi is directly proportional to the instantaneous value of the total lines of magnetic flux issuing from the face of that pole.

(It will be assumed throughout this specification that the gaps be- 12 in a clockwise direction, as viewed in Fig. 2, and winding I, produces in pole 14 flux having a direction away from core 22 toward the closed magnetic circuit. Similarly, the two primary windings E and E, are wound whereby with the potential of terminal 26 being positive with respect to terminal 27, winding E, produces magnetic flux in the closed magnetic circuit in a counterclockwise direction, while winding E produces in pole 16 flux having a direction from the closed magnetic circuit toward the gap D and core 22.

Assuming that the normal direction of electric power flow in the transmission line conductors 30 and 31 is from left to right as shown in Figs. 1 and 2, current will be conducted to the right by conductor 30 and to the left by conductor 31 while 30 is positive with respect to 31. The potential transformer 33 and current transformers 28 and 29, as indicated in Figs. 1 and 2, are so coupled to the conductors 30 and 31 that for the aforesaid coincident instantaneous voltage polarity and current directions in the transmission line, terminal 26 will be positive with respect to terminal 27 and current will flow from terminal 24, through the series connected I and I windings, and back to terminal and current transformers 28 and 29. During the opposite half cycle of transmission line voltage, exactly the reverse polarities and directions will co-exist.

'The fluxes produced upon energization of primary windings I I E and E establish magnetic fields in the four gaps A, B, C, and D. These magnetic fields interact in rotor 23 to create driving torque for actuating the rotor. The torque producing phenomena will now be investigated with reference to Fig. 3.

.In Fig. 3 a cup-shaped current conducting rotor 37 is shown disposed for rotation about an axis 38 located at its center. A pair of poles 39 and 40 represent sources of two out-of-phase alternating magnetic fields through which rotor 37 is movable. Poles 39 and 40 are asymmetrically disposed with respect to axis 38, that is, the vertical centerlines of both of their pole faces are not coplanar with the axis of rotation. As indicated in Fig. 3, the surface of rotor 37 and the faces of poles 39 and 40 are concentric, and the magnetic flux issuing from each pole face is substantially perpendicular to the rotor surface.

A current conductor of unit length in an alternating magnetic field will experience a force (1 being avector quantity since force has both magnitude and direction) which is equal to the vector product of the current i flowing inthe conductor and the magnetic fiux density B. Applying this fundamental principle to the situation illustrated in Fig. 3, it will be observed that where the flux tween rotor surface and pole faces are sufficiently short to warrant neglecting leakage flux.) The current 'i flowing in the portion of rotor 37 intersecting flux p is actually the eddy current i' set up by voltage which is induced in the rotor by the alternating magnetic field from pole 40. Since the path of this current is perpendicular to the direction of the flux, the magnitude of the vector product of current and flux is the same as the algebraic product of their magnitudes. Thus, the general expression for the force on rotor 37 at pole 39 becomes f ocei' rp where e is a unit vector operator which supplies direction to the quantity i The direction is in accordance with the conventional right-hand-screw rule.

Similarly, the general expression for the force on rotor 37 at pole 40 is where is the instantaneous flux issuing from the face of the pole 40 and i is the eddy current in rotor 37 resulting from the voltage induced by the alternating flux from pole 39.

These general expressions can be put in more workable form by certain substitutions. In the first place, the instantaneous flux issuing from pole 39 is equal to I sin wt, where t is the maximum magnitude of the alternating flux in pole 39, w is 21r times the frequency of this alternating quantity, and t is time. Also, the instantaneous fiux of pole 40 is equal to I sin (wt-0'), I being the maximum magnitude of alternating flux in pole 40 and 0' representing a constant positive phase angle by which I is assumed to lag c. It will be assumed, in order to maintain consistent signs throughout this specification, that the positive direction of magnetic flux is always from a pole face toward the rotor.

Since the paths followed by eddy currents in rotor 37 are substantially wholly resistive, the magnitude of these eddy currents will be directly proportional to the induced voltages producing them. Induced voltage, in accordance with Faradays fundamental law of electro-magnetic induction, is proportional to I and causes current flow in a direction tending to oppose the change in flux. For example, at the moment of time when both and are positive but decreasing in magnitude, the eddy current directions will be as indicated in Fig. 3. Another arbitrary directional assumption should be made at this point: positive eddy current will be assumed to flow upward as viewed in Fig. 3, and in accordance with the right-hand-screw rule, positive current and positive flux produce positive force in a direction tending to move rotor 37 clockwise. Accordingly, a representative expression for 1",, is d cos (tar-a) and for i is *I cos wt.

By using the above relationships, the general expressions 1 and 2 become respectively (5) Tcce hd sin Expression in connection with the directional assumptions previously made clearly demonstrates that result- 'ant torque tends to drive rotor 37 from the pole of leading flux toward the pole of lagging ilux. If the flux of pole 40 were to become leading, sin a would of course be negative and the torque would then be negative or counterclockwise, still toward the pole of lagging flux. Expression 5 further demonstrates that some phase displacement 4 between the magnetic fields of poles 39 and 40 is necessary to produce torque.

Another observation can be made at this point. The above described torque producing elfect can be obtained with two poles disposed at any radial interval with respect to the axis of rotation other than an interval of zero or 180 degrees. But poles located in a common plane with the axis 38, or more specifically, poles having symmetrical faces whose overlaps with the rotor are bisected by a common axial plane, will produce no resultant torque. This is due to the fact that at such locations in effect the net eddy current magnitude is zero.

The expression Eco sin 0' for resultant torque is equivalent to the vector product of and o, where direction is physically from the pole of leading flux to the pole of lagging flux. Thus expression 5 can be written (6) iocsxa' It should now be apparent that for a 4-pole electromagnetic relay structure such as shown in Figs. 1 and 2, the general expression for net torque is:

where the subletters refer to the gapsbetween core and pole faces to identify the respective magnetic fields. In utilizing expression 7, it must be kept in mind that the chosen positive direction of flux is from pole face toward the core, that torque produced by positive fluxes from adjacent poles is actually in a direction toward the pole of lagging flux, and that the positive direction of torque is clockwise, i. e., from gap A to B, B to C, etc.

In order to convert the general expression 7 to units of transmission line voltage and current, it is necessary in respect to each embodiment of the invention to investigate the composition of the magnetic fields in the various gaps in terms of flux components attributable to the various windings on stator 12. A specific investigation of this nature will be preceded by a general consideration of magnetic circuits, with reference to Figs. 4a, 4b and 4c, and in this manner a helpful approach for making the detail analysis can be evolved.

Fig. 4a illustrates a simple magnetic circuit comprising a magnetizable member 41 having spaced apart outer legs 42 and 43 and a central leg 44. A main winding 45 of N turns is wound on the central leg 44 and is supplied with alternating energizing current i. A shading winding 46 of N turns is mounted on outer leg 43. There are identical airgaps 47 and 48 in the magnetic circuits which include outer legs 42 and 43 respectively. Thus, the fiux produced by energizing current flowing in main winding 45 can follow two parallel magnetic paths; one path comprising outer leg 42, airgap 47, and the common central leg 44; the other path comprising outer leg 43, through shading winding 46, airgap 48, and the common central leg 44. It will be assumed that leakage flux and losses may be neglected and that no magnetic saturation of the magnetizable material occurs.

Consider first the magnetic path of outer leg 42 as shown in Fig. 4a. The flux m in this path is equal to the M. M. F. (Ni) provided by main winding 45 divided by the reluctance R of the path. The general formula for magnetic reluctance is where l is the length of magnetic path, A is its cross sectional area, and a is the permeability of the material.

Since the permeability of magnetizable material often is more than times greater than the permeability of air, the reluctance provided by legs 42 and 44 can be neglected, and the total reluctance of the magnetic path under considerationcomprises essentially the reluctance of the airgap 47. This reluctance will be designated by the constant K, the magnitude of which is dependent upon the airgap configuration. The flux o; is in phase with the energizing current i.

Consider now the magnetic path of outer leg 43 as shown in Fig. 4a. Here the flux e, is equal to the sum of the M. M. F. (Ni) provided by the main winding 45 and the M. M. F. (N,i,) due to current i circulating in shading winding 46, this sum being divided by the reluctance K, of airgap 48. Re,

( a2 s s The instantaneous flux is actually 4*, sin (wt-a) where 1, is the maximum magnitude of alternating flux in the path under consideration and U is a positive angle by which r, is assumed to lag or i. The current i. in shading winding 46 is equal to the voltage induced in this winding divided by its resistance R,. The induced voltage by Faradays law is and therefore NJ, is equal to Let R, equal K,, a constant which is dependent upon the amount of resistance per turn of shading winding 46. Substitution in Equation 8 gives:

(9) Ni=[K,, sin (uta) +K, cos (wt-c010,

Recalling that cos (wt-a) equals sin (01-1-90'), the expression within the brackets of Equation 9 can be put in vectorial form, and Equation 9 becomes:

Equation 10, which has been illustrated vectorially in Fig. 4b, demonstrates that the shading coil 46 in efiect introduces inductive reluctance K, into the magnetic circuit thereby retarding the buildup of flux in outer leg 43 with respect to the M. M. F. producing it. In other words, the ampere-turns of main winding 45 produce in central leg 44 total flux 3; comprising two out-of-phase components: a principal component in the unshaded path provided by outer leg 42; and the lagging component 3, in the parallel shaded path of outer leg 43. The shading winding 46 may be thought of as retarding a component of the total magnetic flux produced by main winding 45. The total flux Q, will lag the M. M. F. producing it by a phase angle less than a.

From the foregoing relationships, it is possible to draw certain analogies and to construct an electric circuit which is equivalent to the magnetic circuit of Fig. 4a. The following observations can be made: M. M. F. (Ni) is analogous to electric voltage V, magnetic flux is analogous to electric current I, airgap reluctance K. is analogous to resistance R and shading coil reluctance K is analogous to inductive reactance X Thus, the electric circuit shown 9 in Fig. 4c is a valid representation of the magnetic circuit of Fig. 4a.

For the purpose of a detailed analysis of the magnetic fields in each gap of the 4-pole electromagnetic relays illustrated in Figs. 1 and 2, it is convenient, for reasons which will become obvious hereinafter, to utilize the analogies derived above and to visualize equivalent electric circuits. Such equivalent circuits have been illustrated on the second sheet of the drawings.

Figs. a and 6a, which are schematic representations of the Fig. 1 embodiment of my invention, show in addition to the physical locations of shading windings S and 8,, the locations of primary windings E E 1;, and I respectively. Figs. 5b and 6b are equivalent electric circuits of Figs. 5a and 6a respectively. In Figs. 5b and 6b each symbol designating resistance or inductive reactance is identified by a reference character corresponding to the appropriate airgap or shading winding counterpart. From inspection of the equivalent circuits, the current paths can be readily ascertained, and these paths have been traced by broken lines.

In Fig. 5b the current path through resistors A and C is labeled k to represent a principal component of magnetic flux produced upon energization of the primary windings E and E and the path through reactance S resistors D and B, and reactance S is labeled o to represent a lagging component of flux produced upon energization of the same primary windings. Similarly, in Fig. 6b the current path through resistors A and C is labeled Q; to represent a principal component of magnetic flux produced upon energization of the primary windings I and I and the path through reactance 8,, resistors B and D, and reactance S, is labeled Q; to represent a lagging component of flux produced by the same windings. It is apparent that the shading windings S and S, act to retard a portion or component of the total magnetic flux produced by each of the primary windings. Another portion or component of the total magnetic flux produced by each primary winding follows a path which does not pass through either one of the shading windings.

The equivalent magnetic paths of a Q' Q and Q; have been reproduced by corresponding broken lines in Figs. 5a and 6a. Arrow heads have been included to indicate instantaneous flux directions, assuming an arbitrary instant of time wherein the potential of input terminal 26 is positive with respect to terminal 27 and energizing current is flowing in primary windings I, and I, from input terminal 24 to terminal 25. Now by inspection, the flux issuing from each pole face in the Fig. l arrangement will be seen to be as follows:

$ =2Qg+2@ @B='-2@'E+2QI; @c=-2@ -2@ and d =2d ';-2 I It can be observed at this point that the magnetic field established in each gap comprises flux components dependent upon each of the energizing quantities supplied to the two sets of interconnected primary windings. Furthermore, the magnetic fields in adjacent gaps comprise different or out-of-phase flux components attributable to the same energizing quantity.

The magnetic flux components in gaps A, B, C, and D, as set forth above, can be substituted into the general torque expression 7. Upon reducing by conventional vector algebra, the following torque expression for the Fig. 1 embodiment of my invention is derived:

The Fig. 2 embodiment of my invention is schematically represented in Figs. 7a and 8a which illustrate in addition to the physical location of shading windings S and S, the locations of primary windings E E I, and 1, respectively. Figs. 7b and 7c are equivalent electric circuits of Fig. 7a, and Figs. 8b and 8c are equivalent electric circuits of Fig. 8a. From inspection of these equivalent circuits, current paths are readily ascertained and have been traced on the figures by broken lines.

In Fig. 7b, the current path. through resistors A and B is labeled o to represent a principal component of magnetic flux produced upon energization of primary winding E The lagging component of current (flux) from E is entirely in the body of the stator and does not pass through a resistor (gap), and accordingly it does not enter into the rotor torque-producing picture. Incidentally, shading windings S and S; are designed to offer sulficient reluctance K, to prevent this lagging component from saturating the magnetizable stator. In Fig. 7c the current path through resistors D and C is labeled Q to represent a principal component of magnetic flux produced upon energization of primary winding E and the paths through resistor D and the parallel branches comprising resistor A in series with reactance S and resistor B in series with reactance S are each labeled I to represent lagging components of flux produced by primary winding E Similarly, in Fig. 8b the current path through resistors D and C is labeled o to represent a principal component of magnetic flux produced upon energization of primary winding I In Fig. 8c the current path through resistors A and B is labeled Q to represent a principal component of magnetic flux produced upon energization of primary winding I and each of the paths comprising the parallel branches of reactance S, in series with resistor D and reactance S in series with resistor- C, the parallel branches connected in series with resistor B, is labeled it}, to represent lagging components of flux produced by primary winding 1:. It is apparent that shading windings S and 8; act to retard a portion of the total magnetic flux produced by each of the primary windings E1, E2, I1, I2.

The equivalent magnetic paths of a 45: @3 Q and F are represented by corresponding broken lines in Figs. 7a and 8a. Arrow heads have been included to indicate instantaneous flux directions for the same arbitrary instant of time that was assumed above in connection with Figs. 5a and 6a. Now by inspection, the fluxes issuing from the pole faces in the Fig. 2

arrangement will be seen to be as follows:

.4= E "s 1 s= s 's' "r C EZ I1+ I2 and D=E2+2E2+[1+Q'I2' It can-be observed at this point that the magnetic field established in each gap comprises components of flux dependent upon each of the energizing quantities supplied to the primary windings. Furthermore, the magnetic fields in adjacent gaps comprise different or out-of-phase components of flux dependent upon the same energizing quantity. In addition, it will be noted that the instantaneous direction of flux produced in a pole by a primary winding disposed on that pole corresponds to the instantaneous direction of flux produced in the adjacent pole by the associated primary winding. In other words, the fluxes produced by interconnected primary windings in adjacent poles, one of said primary windings being located on one of said adjacent poles, have the same relative instantaneous directions.

The components of magnetic flux in gaps A, B, C, and D, as set forth above, can be substituted into the general torque expression 7. Upon reducing by conventional vector algebra, the following expression of net torque for the Fig. 2 embodiment of my invention is derived:

Expressions 11 and 12 can be readily converted to units of transmission line voltage and current. It will be recalled that the vector product of two flux vectors is equal to e times the product of their magnitudes and the sine of the angle therebetween. Furthermore, assuming no saturation, flux magnitude is directly proportional to the magnitude of the M. M. F. or ener- 11 gizing quantity producing it. Thus, c c' o e and Q are each proportional to the transmission line current -I which furnishes the energizing current via current transformers 28 and 29 and input terminals 24 and 25 for the series connected primary winding I and I producing these fluxes. The principal components of current produced flux Q Q and Q are each in phase with the current I, while the lagging components t; and 9' lag their respective principal components by constant angles determined by the effective reluctance of their respective shaded paths.

In the same fashion, Q I d and I are each proportional to the transmission line voltage E which provides by means of potential transformer 33, network 32 and input terminals 26 and 27 energizing current for the interconnected primary windings E and E, producing these fluxes. The principal components of voltage produced flux o Q and 4 are each in phase with the energizing current and this current is displaced from the voltage E by a constant phase angle 0. It will be assumed that a positive angle represents lagging energizing current. As described hereinbefore, this angle is determined by the phase shifting network 32. The lagging components I and I lag their respective principal components by constant angles determined by the effective reluctance of their respective shaded paths.

The foregoing relationships are illustrated vectorially in Fig. 9 for the Fig. 1 embodiment of my invention. As shown in this figure, transmission line voltage E is the reference. Transmission line current I is shown lagging E by a positive power factor angle 8. The angle 0 by which I lags b; is the same as the corresponding angle by which 1 lags c since as can be seen by comparing Figs. 5b and 6b, these flux components follow 7 identical shaded and unshaded paths and therefore are affected by the same reluctances. For the same reason, the magnitude ratios of Q; to Q} and of to F are equal.

Utilizing the information contained in the preceding three paragraphs, expression 11 can be written where K is a predetermined constant deter-mined by the product of sin 0' and the proportionality factors relating o and I to E, K is a predetermined constant corresponding to K except relating to I, and K is a predetermined constant determined by the product of the proportionality factors relating o to E and relating t to I. It can be shown by trigonometric identities that sin (5+a-0) sin (0+o'fi)=2 cos a sin 8-6). Letting the constant quantity 2K cos o'=K, expression 13 is simplified, and the resulting torque expression in terms of transmission line quantities for the Fig. 1 embodiment of the invention becomes By similar substitutions and simplification in regard to expression 12, the following resulting torque expression in terms of transmission linequantities for the Fig. 2 embodiment of the invention can be derived:

(For the sake of expediency in connection with the utilization of these expressions hereinafter, the same reference characters K K, and K have been used to designate corresponding constants in both expressions l4 and 15, although the actual numerical magnitudes represented by these constants in expression probably will be different than in expression 14. Such difference is attributable to the fact that, since the windings are arranged differently in the two illustrated embodiments of the invention, the corresponding magnetic paths do not have identical reluctances.)

Analysis of expressions 14 and 15 clearly demonstrate that with the windings arranged and connected on stator 12 in accordance with my invention, the net driving torque produced in rotor 23 comprises a component proportional to the square of transmission line voltage E, a component proportional to the square of transmission line current I, and a component dependent upon the product of the respective magnitudes of E and I and a function of the phase displacement therebetween. Thus, both illustrated embodiments of the invention are distance relays having offset mho operating characteristics. The Fig. 1 embodiment (expression 14) is arranged whereby the voltage squared component of torque is negative and the current squared component is P tive, and consequently positive torque can be developed with zero voltage. 011 the other hand, the Fig. 2 embodiment (expression 15) is arranged whereby both the voltage squared and current squared components of torque are negative and no positive torque is produced with zero voltage.

It will be assumed that positive or clockwise movement of rotor 23 is required for relay operation. Whenever the net driving torque is positive, the relay operates to perform its preselected control function, and whenever the net driving torque is negative, no operation is obtained. The condition of zero torque, therefore, defines the operating limits of the relay. Thus, by equating the torque expressions l4 and 15 to zero, dividing through by I, and rearranging, the following two equa tions describing the operating characteristics of the relay embodiments shown respectively in Figs. 1 and 2 are derived:

where Z is the apparent impedance of the transmission line as seen by the relay, i. e., the ratio of transmission line voltage E to transmission line current I as reflected by potential transformer 33 and current transformers 28 and 29.

These operating characteristics can be conveniently illustrated by conventional impedance diagrams as shown 1n igs. l0 and 11. The origin of each impedance diagxafn represents the point where the potential and curr nt transformers which supply the relay are coupled to the transmission line, while the abscissa R and the ordinate jX describe values of resistance and inductive reactance respectively as determined by the vectorial relationship, between transmission line voltage and current measured by these transformers. Both coordinates R and IX are-scaled equally and in the same units, such as ohms.

The circle identified in Fig. 10 by the reference character Z, represents the loci of apparent impedance values which define the operating range of Fig. l offset mho distance relay. Whenever the apparent impedance Z, as indicated by the ratio of the voltage and current quantities supplied to the relays by the potential and current transformers, becomes less than 2,, the net driving torque of rotor 23 is positive and substantially instantaneous relay operation is obtained.

The circle Z, in Fig. 10 has been drawn by rearranging the quadratic Equation 16 and by plotting the resulting operating characteristic equation:

b b 1 K, -nn V (in) 's.

where b=K sin (3-0). The angle 0 which is controlled by phase shifting network 32 has been assumed to be a constant negative angle of less than i. e., energizing current in primary windings E and F leads transmission line voltage E. Several interesting observations can be made from Equation 18 Whenever the power factor angle 3 is equal to or 0+180, b=0, and

2K; and r: 3 /11 41 It should now be apparent that Z in Fig. 10 comprises a circle having a radius r and a center displaced from the origin by a vector d whose magnitude is less than r and whose angle is ,B,,,.

If the K 1 term in the torque expression 14 above were absent, the Fig. 1 embodiment of my invention would comprise simply a conventional mho relay having an operating characteristic which could be represented by the equation 2-; sin (8-0) as is illustrated by circle f(d) in Fig. 10. But with the arrangement and connections of windings shown in Fig. 1 and described hereinbefore, the mho relay is modified and there is included a torque component KgI opposing the K E' torque component. As a result, the mho circle is enlarged to include the origin, and positive relay operation can be obtained with zero transmission line voltage.

The circle identified in Fig. 11 by the reference character Z represents the loci of apparent impedance values which define the operating range of the Fig. 2 offset mho distance relay. Whenever the magnitude and angle of apparent impedance Z become such that the magnitude falls between the predetermined limiting magnitudes at the particular angle as established by circle 2;, net driving torque of rotor 23 is positive and substantially instantaneous relay operation is obtained.

The circle Z, in Fig. 11 has been drawn by solving quadratic Equation 17 and plotting the resulting operating characteristic equation:

where fi 0=-(fl --0). Assuming that p, is the more positive angle, relay operation can occur only when 51 fl fl2 0r (fl1+ fi (fi2+ For other .values of p, the square root term in Equation 19 will be imaginary, thereby indicating that no condition of zero torque can exist. Whenever the power factor angle is exactly equal to or 3,, Equation 19 reduces to or Z, as shown in Fig. 11. At fl +180 and p +180,

Z =Z and the same points are defined. With 5 equal to 0+180 (p in Fig. 11), b=-K and the maximum 14 and minimum values of 2, become d+r and d-r respectively, where and r= /d --Z, With 5 equal to 0, b=K and Z =d+r which identify the same two points. It should now be apparent that Z in Fig. 11 comprises a circle of 'radius r having a center displaced from the origin by a vector Zi whose magnitude is greater than r and whose angle is p If the K 1 term in the torque expression 15 above were absent, the Fig. 2. embodiment of my invention would comprise simply a conventional mho relay having an operating characteristic which could be represented by the equation as is illustrated in Fig. 11 by the circle f(d). But with the arrangement and connections of windings shown in Fig. 2 and described hereinbefore, the mho relay is modified and there is included a torque component K 1 aiding the K E torque component. As a result, the mho circle is contracted to exclude the origin, and the relay will not operate when transmission line voltage is zero.

While I have shown and described a preferred form of my invention by way of illustration, many modifications will occur to those skilled in the art, I therefore contemplate by the claims which conclude this specification to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A circuit controlling electromagnetic induction type relay responsive to predetermined phase and magnitude relationships between two input alternating electric quantities comprising, a magnetizable stator providing a magnetic loop and having a plurality of salient poles projecting therefrom, a magnetizable member spaced apart from the extremities of said poles to define therewith a plurality of gaps, a circuit controlling current conducting rotor disposed for rotation through said gaps in a direction generally transverse to the magnetic fields between said poles and said member, a plurality of magnetic flux producing primary windings on said stator energizable by the two input quantities for establishing magnetic fields in said gaps, and a plurality of shading windings arranged on said stator to retard only a portion of the total magnetic flux produced by each of said primary windings, said magnetic fields interacting in said rotor to produce driving torque, said windings being arranged whereby said driving torque comprises a component proportional to the square of the magnitude of one of the input quantities, a component proportional to the square of the magnitude of the other input quantity and a component proportional to the product of the respective magnitudes of the two input quantities and a function of the phase displacement therebetween.

2. An electromagnetic distance relay adapted to be energized by alternating current and voltage derived from an electric power system comprising, a magnetizable structure providing a closed magnetic path and having only four poles projecting therefrom, a magnetizable member disposed in spaced apart relation with the faces of said poles to provide a common link in the magnetic circuit "for magnetic fluxes issuing from the faces. of said poles, a current conducting circuit controlling element extending into the gaps formed by said magnetizable member and pole faces for movement in a direction generally parallel to said pole faces, a pair of shading windings on said structure, a first pair of magnetic flux producing windings on said structure connected for energization by the alternating voltage, and a second pair of magnetic flux producing windings on said structure connected for energization by the alternating current, said windings being arranged when energized to produce driving force in said element dependent on where K, K and K are constants, E and I are the alternating voltage and current supplied to said first and second pairs of windings respectively, {3 is the phase angle between E and I, and is a constant phase angle between E and the energizing currentflowing in said first pair of windings.

3. An electromagnetic distance relay adapted to be energized by alternating current and voltage derived from an electric power system comprising, a magnetizable structure providing a closed magnetic path and having only four poles projecting therefrom, a magnetizable member disposed in spaced apart relation with the faces of said poles to provide a common link in the magnetic circuit for magnetic fluxes issuing from the faces of said poles, a current conducting circuit controlling element extending into the gaps formed by said magnetizable member and pole faces for movement in a direction generally parallel to said pole faces, a pair of shading windings on said structure, a first pair of magnetic flux producing windings on said structure connected for energization by the alternating voltage, and a second pair of magnetic flux producing windings on said structure connected for energization by the alternating current, said windings being arranged when energized to produce driving force in said element dependent on K E -l-K l -l-KEl cos (ti-0) where K, K, and K are constants, E and I are the alternating voltage and current supplied to said first and second pairs of windings respectively, 3 is the phase angle between E and I, and 0 is a constant phase angle between E and the energizing current flowing in said first pair of windings.

4. In a circuit controlling electromagnetic induction type relay responsive to predetermined phase and magnitude relationships between two alternating electric quantities, a magnetizable stator providing a magnetic loop and having four spaced apart poles projecting therefrom, a magnetizable member spaced apart from the extremities of said poles to define therewith four gaps, a circuit controlling current conducting rotor axially supported for rotation through said gaps in a direction generally transverse to the lines of magnetic flux between said poles and said member, two pairs of input terminals respectively supplied by the two alternating electric quantities, at least one pair of magnetic flux producing windings mounted on said stator and connected directly to a first one of said pairs of input terminals, at least another pair of magnetic flux producing windings mounted on said stator and connected directly to the other pair of input terminals, and a plurality of shading windings on said stator for retarding the fluxes encompassed thereby, said windings being arranged to establish in at least two of said gaps two out-of-phase components of flux dependent upon one of the electric quantities and to establish in at least two of said gaps two out-of-phase components of flux depend ent upon the other electric quantity.

5. In a circuit controlling electromagnetic induction type relay responsive to predetermined phase and magnitude relationships between two input alternating electric quantities, a magnetizable stator providing a magnetic loop and having only four spaced apart poles projecting therefrom, a magnetizable member spaced apart from the extremities of said poles to define therewith four gaps, a circuit controlling current conducting rotor axially supported for rotation through said gaps in a direction generally transverse to the magnetic fluxes between said poles and said member, an even number of magnetic flux producing primary windings located on said stator and interconnected in pairs for energization by the two input quantities to establish in each of said gaps magnetic fluxes 16 dependent upon each of the input quantities, and two shading windings located on said stator to retard a component of the flux produced by each of said pairs of interconnected primary windings in a plurality of said gaps not exceeding three.

6. A circuit controlling electroresponsive relay comprising, alternating voltage input terminals, alternating current input terminals, a magnetizable stator providing a magnetic loop andhaving four poles projecting therefrom, a magnetizable member spaced apart from the extremities of said poles to define therewith four gaps, a circuit controlling current conducting rotor disposed for rotation through said gaps in a direction generally trans verse to the magnetic fluxes in said gaps, a plurality of primary windings, a first group of at least two of said primary windings being connected for energization to said alternating voltage input terminals and arranged on said stator jointly to produce difierent components of magnetic flux in at least two of said gaps, a second group of at least two of said primary windings being for energization to said alternating current input terminals and arranged on said stator jointly to produce diflerent components of magnetic flux in at least two of said gaps,

and at least two shading windings on said stator for retarding one component of flux produced by each group of primary windings with respect to the associated flux component.

7. In a circuit controlling electromagnetic induction relay responsive to predetermined phase and magnitude relationships between two input alternating electric quantities, an axis, a magnetizable core, a magnetizable stator having a body which provides a closed magnetic circuit and having a plurality of poles terminating in faces spaced from said core to form a plurality of gaps disposed at generally radial intervals with respect to said axis, a circuit controlling eleetroconductive armature pivotally mounted for rotation about said axis and having a portion spaced from said axis disposed in said gaps in overlapping relation with said pole faces, a plurality of primary windings connected to be energized by the two input quantities for producing magnetic fluxes in said stator and gaps, at least two of said primary windings being disposed on the body of said stator, and a plurality of shading windings on said stator for retarding the fluxes traversing paths therethrough, said windings being arranged to establish in at least two of said gaps formed by pole faces whose overlaps with said armature are bisected by different axial planes two out-of-phase components of flux dependent upon one of the input quantities and to establish in at least two of said gaps formed by pole faces whose overlaps with said armature are bisected by different axial planes two out-of-phase components of flux dependent upon the other input quantity.

8. In a circuit controlling electromagnetic induction relay responsive to predetermined phase and magnitude relationships between two input alternating electric quantities, an axis, a magnetizable member, a magnetizable frame providing a closed magnetic circuit and having a plurality of poles whose extremities are spaced from said member to define therewith a plurality of gaps located at generally radial intervals with respect to said axis, a circuit controlling induction element axially supported for movement through said gaps in a direction generally parallel to the extremities of said poles, a plurality of primary windings connected to be energized by the two input quantities for producing magnetic fluxes in said frame and gaps, and a plurality of shading windings on said frame for retarding the fluxes encompassed thereby, a plurality not exceeding three of said windings being located on the poles of said frame, said windings being arranged to establish in at least two of said gaps which are not intersected by a common plane including said axis two out-of-phase components of flux dependent upon one of the input quantities and to establish in at least two of said gaps which are not intersected by a common plane including said axis two out-oE-phase components of flux dependent upon the other input quantity.

9. In an electromagnetic relay, alternating current input terminals, alternating voltage input terminals, a magnetizable core disposed on an axis, a stator having four salient poles spaced from said core to define therewith four gaps, a circuit controlling electroconductive armature disposed for movement through said gaps, a first pair of magnetic flux producing windings connected to said current input terminals, a second pair of magnetic flux producing windings connected to said voltage input terminals, and a pair of shading windings, said winding being disposed on said stator to establish in a pair of said gaps which are asymmetrical with respect to said axis two out-of-phase components of flux produced by said first pair of windings and to establish in another pair of said gaps which are asymmetrical with respect to said axis two out-of-phase components of flux produced by said second pair of windings.

10. A circuit controlling electromagnetic relay responsive to predetermined phase and magnitude relationships between two input alternating electric quantities comprising, a magnetizable frame providing a continuous magnetic path and having four poles effectively separating said magnetic path into four sections, a magnetizable member spaced apart from the extremities of said poles to define therewith four gaps, a circuit controlling current conducting rotor disposed for rotation through said gaps in a direction generally transverse to the magnetic fluxes between said poles and said member, two shading windings located on alternative poles for retarding the magnetic fluxes encompassed thereby, two primary windings located on alternative sections of said magnetic path and energizably connected in series circuit relation to one of the two input quantities for producing in said magnetic path opposing magnetic fluxes, and two primary windings located on intermediate sections of said magnetic path and energizably connected in series circuit relation to the other input quantity for producing in said magnetic path opposing magnetic fluxes.

11. A circuit controlling electromagnetic relay comprising, alternating voltage input terminals, alternating current input terminals, a magnetizable frame providing a closed magnetic path and having four poles projecting therefrom effectively to divide said magnetic path into four quarters, a magnetizable core spaced apart from the extremities of said poles to define therewith four gaps, a circuit controlling'electroconductive armature axially supported for rotation through said four gaps, two shading windings located on non-adjacent poles, a first primary winding connected to said alternating voltage terminals and arranged on the quarter of said magnetic path disposed between first and second adjacent poles for producing magnetic flux in said magnetic path, a second primary winding connected to said alternating current terminals and arranged on the quarter of said magnetic path disposed between said second and a third adjacent poles for producing magnetic flux in said magnetic path, a third primary winding connected to said alternating voltage terminals and arranged on the quarter of said magnetic path disposed between said third and a fourth adjacent poles for producing magnetic flux in said magnetic path in a direction opposing the magnetic flux produced by said first winding, and a fourth primary winding connected to said alternating current terminals and arranged on the quarter of said magnetic path disposed between said fourth and said first adjacent poles for producing magnetic flux in said magnetic path in a direc tion opposing the magnetic flux produced by said second primary winding.

12. In an electromagnetic distance relay adapted to be energized by alternating current and voltage, a magnetizable frame providing a continuous magnetic path and having four poles effectively defining four consecutive sections of said magnetic path, a magnetizable member spaced apart from the extremities of said poles to define therewith four gaps, a circuit controlling current conducting rotor disposed for rotation through said four gaps in a direction generally transverse to the magnetic fluxes issuing from'the extremities of said poles, first and second shading windings arranged respectively on alternative sections of said magnetic path for shading the magnetic fluxes in these sections, first and second primary windings located respectively on one of the intermediate sections of said magnetic path and on one of the poles defining the remaining section of said magnetic path and connected in series circuit relation for energization by the alternating current for producing in the pole of said second primary winding and in the adjacent pole defining said one intermediate section magnetic fluxes having corresponding instantaneous directions, and third and fourth primary windings located respectively on said remaining section and on one of the poles defining said one intermediate section and connected in series circuit relation for energization by the alternating voltage to produce in the pole of said fourth primary winding and in the adjacent pole defining said remaining section magnetic fluxes having corresponding instantaneous directions.

13. An electromagnetic induction relay for performing a control function in response to predetermined phase and magnitude relationships between two electric quantities derived from an alternating current source comprising, a magnetizable stator providing a closed mag netic circuit and having four poles effectively defining first, second, third, and fourth consecutive parts of said magnetic circuit, a magnetizable member spaced apart from the extremities of said poles to define therewith four gaps, a circuit controlling current conducting rotor disposed for rotation through said four gaps, first and second shading windings arranged respectively on said first and third parts of said magnetic circuit for shading the magnetic fluxes traversing these parts, first and second primary windings located respectively on said second part of said magnetic circuit and on one of the poles defining said fourth part of said magnetic circuit and connected for energization in series circuit relation to one of the two electric quantities for producing in said one pole and in the adjacent pole defining said second part magnetic fluxes having the same relative directions, and third and fourth primary windings located respectively on said fourth part and on the pole not adjacent to said one pole and connected for energization in series circuit relation to the other electric quantity for producing in the pole of said fourth primary winding and in the adjacent pole defining said fourth part magnetic fluxes having the same relative directions.

14. In a circuit controlling electromagnetic induction type relay responsive to predetermined phase and magnitude relationship between two input alternating electric quantities, a magnetizable stator providing a magnetic loop and having four poles projecting therefrom, a magnetizable member spaced apart from the extremities of said poles to define therewith four gaps, a circuit controlling current conducting rotor disposed for rotation through said gaps in a direction generally transverse to the magnetic fields between said poles and said member, four magnetic flux producing primary windings on said stator interconnected in pairs for energization by the two input quantities, and shading means on said stator for retarding a portion of the flux produced by each of the pairs of interconnected primary windings, whereby the total flux produced by each of said pairs comprises a principal and a lagging component, said windings being arranged to produce: in the gap associated with a first pole a magnetic field comprising the principal component of one pair aiding the principal component of the other pair, in the gap associated with a second pole adjacent said first pole a magnetic field comprising the lagging component of said one pair opposing the lagging component of said other pair, in the gap associated with a third pole adjacent said second pole a magnetic field comprising the principal component of said other pair aiding the principal component of said one pair, and in the gap associated with a fourth pole adjacent said first and third poles a magnetic field comprising the lagging component of said other pair opposing the lagging component of said one pair.

15. In a circuit controlling electromagnetic induction type relay responsive to predetermined phase and magnitude relationships between two input alternating electric quantities, a magnetizable stator providing a magnetic loop and having four poles projecting therefrom, a magnetizable member spaced apart from the extremities of said poles to define therewith four gaps, a circuit controlling current conducting rotor disposed for rotation through said gaps in a direction generally transverse to the magnetic fields between said poles and said member, four magnetic flux producing primary windings on said stator interconnected in pairs for energization by the two input quantities, and shading means on said stator for retarding portions of the flux produced by each of the pairs of interconnected primary windings, whereby the total flux produced by each of said pairs comprises principal and lagging components, said windings being arranged to produce: in the gap associated with a first pole a magnetic field comprising a principal component of one pair aiding a principal component and opposing a lagging component of the other pair, in the gap associated with a second pole adjacent said first pole a magnetic field comprising a principal and a lagging component of said other pair aiding principal and lagging components of said one pair, in the gap associated with a third pole adjacent said second pole a magnetic field comprising a principal component of said other pair aiding a principal component and opposing a lagging component of said one pair, and in the gap associated with a fourth pole adjacent said first and third poles a magnetic field comprising a principal component and a lagging component of said one pair aiding principal component and lagging components of said other pair.

16. A circuit controlling electromagnetic relay comprising, alternating voltage input terminals, alternating current input terminals, a magnetizable frame having a body which provides a closed magnetic path and having four salient poles effectively separating the body into a four sections, a magnetizable core spaced apart from the extremities of said poles to define therewith four gaps, a

circuit controlling electroconductive armature axially supported for rotation through said four gaps, a plurality of primary windings mounted on said frame, at least one of said primary windings being located on each section of the body of said frame, at least one pair of said primary windings being connected to said alternating voltage input terminals for producing magnetic flux in each one of said gaps, at least another pair of said primary windings being connected to said alternating current input terminals for producing magnetic flux in each one of said gaps, and a pair of shading windings mounted on non-adjacent poles of said frame for retarding all of the magnetic fluxes in the two associated gaps.

17. A circuit controlling electromagnetic relay comprising, alternating voltage input terminals, alternating current input terminals, a magnetizable frame having a body which provides a closed magnetic path and having four salient poles effectively separating the body into four sections, a magnetizable core spaced apart from the extremities of said poles to define therewith four gaps, a circuit controlling electrooonductive armature axially supported'for rotation through said four gaps, first and second pairs of primary windings mounted on said frame, one winding of said first pair being located on a first section of the body of said frame and the other winding of said first pair being located on one pole of said frame, one winding of said second pair being located on a second section of said body and the other winding of said second pair being located on the pole which is not adjacent to said one pole, said first pair of primary windings being connected to said alternating voltage input terminals for jointly producing magnetic fluxes in all of said gaps and magnetic flux entirely in said body, said second pair of primary windings being connected to said alternating current input terminals for jointly producing magnetic fluxes in all of said gaps and magnetic'fiux entirely in said body, and a pair of shading windings mounted respectively on third and fourth sections of said body for retarding the magnetic fluxes entirely in said body and less than all of the magnetic fluxes in each one of said gaps.

Verrall May 27, 1941 Warrington July 30, 1946 

